1. Field of the Invention
The present invention relates to a sheet-fed printing apparatus for printing on sheets of printing paper and, more particularly, to a delivery section of the sheet-fed printing apparatus.
2. Description of the Background Art
A sheet-fed printing apparatus for printing on sheets of printing paper comprises a delivery section (or a paper discharge section) for receiving a stack of printed sheets. FIG. 7 is a partial sectional view of a delivery section 110d and its surrounding parts in a conventional sheet-fed printing apparatus 110. The delivery section 110d comprises a delivery table 102 for placing thereon a printed sheet pa discharged from a chain delivery 101 for transporting printed sheets. The printed sheet pa gripped by a gripper 103 carried around by the chain delivery 101 is released (or dropped) from over the delivery table 102. At this time, the leading edge of the printed sheet pa is hit against a sheet-trapping element 104, whereby the printed sheet pa falls upon the delivery table 102. In this manner, such printed sheets pa are successively stacked in a fixed position, and are referred to as stacked printed sheets ps The delivery table 102 is provided with a vertical movement element 105 for moving the delivery table 102 gradually downwardly each time the number of stacked printed sheets ps increases. This is to provide a constantly fixed distance (or vertical spacing) between the printed sheet pa and the delivery table 102 or the stacked printed sheets ps when the printed sheet pa is discharged.
An operator of the sheet-fed printing apparatus 110 is required to take printed samples out of the stacked printed sheets ps during the printing operation. Since the judgment as to whether or not printed sheets are acceptable and the adjustment of the amount of ink supply are made based on a check of the printed samples, the operator must take out printed samples at suitable sampling intervals while the sheet-fed printing apparatus 110 is in operation.
To this end, the sheet-trapping element 104 in the conventional sheet-fed printing apparatus 110 is capable of an opening movement from a closed position 104a indicated by the dotted lines to an open position 104b indicated by the solid lines. In synchronism with the opening movement of the sheet-trapping element 104, a temporary sheet-receiving element 106 pivots from an inoperative position not shown to an operative position shown in FIG. 7. Then, the printed sheet pa is discharged, with the leading edge thereof lifted up by the temporary sheet-receiving element 106. A printed sheet pb indicated by a dotted line in FIG. 7 is shown in such a lifted position.
Thus, the operator can pick one or some sheets out of the previously stacked printed sheets ps under the printed sheet pa lifted by the temporary sheet-receiving element 106. After the printed samples are taken in this manner, the sheet-trapping element 104 is returned to the closed position 104a indicated by the dotted lines, and the temporary sheet-receiving element 106 accordingly returns to its inoperative position not shown. Then, the printed sheet pb received in the temporary sheet-receiving element 106 is discharged onto the delivery table 102, and is additionally stacked on the previously stacked printed sheets ps.
With the above-mentioned arrangement, the operator can manually take out the printed samples with ease in principle. It is, however, actually difficult for the operator to take out the printed samples quickly from the sheet-fed printing apparatus 110 in high-speed operation. Additionally, the delivery section 110d is often provided with a cover thereon so that the operator cannot easily gain access to movable parts of the delivery section 110d. As an example, the delivery section 110d may be an interlocked cover mounted thereon and is adapted to prevent the sheet-fed printing apparatus 110 from operating when the cover is open. In such a case, the operator cannot take out the printed samples during the printing operation, as discussed above.